| dc.description.abstracteng | The work here presented explores DNA as a potential tool for supramolecular nanoconstructs, controlled self-assembly and the easy synthesis and manipulation of the DNA. Besides this, the introduction of chemical modifications to DNA is presented, which opens up possibilities of several applications such as charge transfer, nanomagnets, catalysis and many more. Important contributions were given and explored by the incorporation of artificial nucleobases and groups into DNA through the solid phase synthesis, where the formation of artificial metal-base pairing in recent years has brought several promising systems to the field with great stability. The concept of DNA branches and junctions based on the insertion of metal-complexes expands the possibilities to produce structures such as DNA nanotubes and cages.
In the first part of this thesis it was described the syntheses and characterization of Pd(II) square-planar complexes with ligands based on a trans-chelating motif which produced self-assembled ring structures upon addition of bis-monodentate bridging ligands. Three or two membered rings were obtained as the product, depending upon the angle produced of the binding site of the bridging ligands added. The structures obtained provided information concerning thermodynamic and kinetic stability as well as further shed light on principles such as maximum site occupancy in supramolecular systems. The characterization of the building blocks and formation of the rings were carried out by NMR spectroscopy and ESI mass spectrometry. The controlled formation of metal complexes by introduction of the 1,2-bis(2-pyridylethynyl)-benzene ligand into a library containing phenathroline and terpyridine ligands together with metal cationic species in a “one pot” system may be useful for future high ordered and metal controlled heteroleptic DNA systems.
The next part of this thesis explored the synthesis of ligands and artificial nucleobases as well as their incorporation into DNA. One of the approaches used also relied upon a trans-chelating building block suitable for solid phase DNA synthesis. This trans motif was internally incorporated into the DNA sequence to further produce square-planar metal-base pairing. The second approach relates to the synthesis of an artificial nucleoside designed to contain the trans-chelating motif pointing outside of the DNA duplex in a perpendicular direction tothe DNA helix to further, upon addition of M(II), allow the formation of interduplex cross-link through metal coordination. The characterization of the ligands was performed by NMR spectroscopy and ESI mass spectrometry, the latter of which was also used to characterize the synthesized DNA strands. Spectroscopic studies based on UV/Vis, thermal analysis, fluorescence and CD spectroscopy were performed to study the formation and properties of the assembled DNA systems. Both unmetallated and metallated species were investigated and the stability of the metal-DNA constructs upon addition of M(II) was evaluated. Additional methods as FRET spectroscopy and ESI mass spectrometry were used to obtain more detail concerning the metal complexation observed, which involved the formation of monomeric or/and dimeric metal-DNA systems. Characterization of the metal-DNA systems and the interduplex cross-link were also pursued by polyacrylamide gel electrophoresis. | de |